A recombinant plasmid containing the 2381-bp promoter region of Japanese flounder tumor necrosis factor (TNF) and green fluorescence protein (GFP) was introduced into zebrafish fertilized eggs by microinjection. GFP was expressed in 2 transgenic zebrafish lines in the heart and around the pharynx under unstressed condition. When embryos were exposed to lipopolysaccharide (LPS), GFP was expressed in the whole zebrafish embryonic surface, and Western blot analysis also showed that the level of the expressed GFP protein in zebrafish embryo was higher at an LPS concentration of 140 μg/ml than at LPS concentrations of 0 and 70 μg/ml. Stimulation with either concanavalin A or phorbol myristate acetate induced weak GFP expression, but stimulation with both of them induced strong expression similar to that induced by LPS. GFP expression peaked 1 hour after stimulation, then gradually decreased. These results indicate that transcription regulated by the Japanese flounder TNF promoter could be under the control of the LPS-recognition system in zebrafish embryos.